Islamist insurgents based in North Caucasus republics such as Dagestan who are seeking their own independent state have vowed to disrupt the Sochi Games in order to undermine Putin.

Two American lawmakers who gave television interviews on Sunday expressed concern that the terrorists would follow up on their threats, according to AFP.

"The threats are real. They are basically calling for attacks on the Olympics. I think you're going to see attempts to do that," said Michael McCaul, chairman of the House Homeland Security Committee.

The Republican, in an interview from Moscow with ABC's "This Week," said Russian authorities were taking the threats seriously, deploying 100,000 security officials to erect a "ring of steel" to secure the Sochi airport, mountain trains and the Games themselves.

If there were attacks, he said, they would more likely be directed at soft targets like transportation.

The congressman added that the diplomatic security corps said it was getting good cooperation from the Russians, and noted that two dozen FBI agents were assigned to the massive sports event.